1. Field of the Invention
This invention relates to an electronic device having keyswitches as data input devices. In particular, it relates to an electronic device which requires high-speed key-judging process in low-speed machine cycle operations.
2. Description of the Related Art
In an electronic device such as an electronic desk calculator, a keyswitch matrix typically is provided as a data input device. An example of inputting of key data using this kind of keyswitch matrix in related art is shown in FIG. 1. In the example, an output port 52 outputs data from a ROM (not shown) through a bus-line 51. Manual data are input by a keyswitch matrix 53. Input lines 54 connect the matrix to the output port 52. Output lines 55 transfer data from the matrix 54, and reference numeral 56 is an input port.
Initially, before data is input to the matrix, a setting cycle operation is carried out for preparing the device to receive data. During the setting cycle, multiple-bit data are fed to bus-line 51 from the ROM (not shown), and predetermined bit positions of the multiple-bit data read from the ROM. correspond to a level "1". These data are latched successively to output port 52 at specified intervals. The data latched to output port 52 are then fed to input line 54 in keyswitch matrix 53. Following this setting cycle, data can be input to the matrix 53. During the input or "read" cycle, the data on output line 55 of keyswitch matrix 53 are latched to input port 56 at specified intervals. These latched data are output to bus-line In this way, data corresponding to the operational state of the keyswitch matrix 53 (hereafter, key-data) connected to one of the input lines 54 can be obtained. These key-data are read after having once been stored in a memory, such as a RAM (not shown). A key-judging process then is carried out in an ALU (arithmetic logic unit)(not shown). During this process, the ALU compares the key-data with predetermined data stored in a memory to identify the key-data. Then, the above type of key-data entry operation is repeated on each input in succession.
Thus, with the structure of the related art described above, in the processing of data on bus-line 51, the entry of key-data for one input line is carried out during both the setting cycle and the "read" cycle. Therefore, the time required for entry of data is longer in an electronic device in which the setting and read cycles are set very slow. Also, in this situation, the time of the key-judging process is longer. For instance, in the case of a solar desk calculator, which uses solar cells, the basic clock signal frequency is set at a low level for low current consumption. For this reason, the number of machine cycles is greater, and the key-judging correspondingly is slower.
As described above there is a drawback in the related art device, in that the key-data entry time (the time necessary for properly entering data through one keyswitch) is too long (two machine cycles) and key-judging cannot be carried out rapidly enough.